The present invention relates to fuel pumps, particularly of the type for supplying fuel at high pressure for injection into an internal combustion engine.
Typical gasoline direct injection systems operate at substantially lower pressure level when compared, for example, to IDI or DI diesel fuel injection systems. The amount of energy needed to actuate the high-pressure pump is insignificant in the total energy balance. However, in a system with a constant output pump and variable fuel demands all of the unused pressurized fuel has to be returned into the low-pressure circuit. A good portion of the energy originally used to pressurize the fuel is then converted into thermal energy and has to be dissipated. Even a relatively modest heat rejection (200-500 Watt) will result in fuel temperature increase (especially if the fuel tank is only partially full) and this will further worsen already serious problems resulting from low vapor pressure of a typical gasoline fuel. Because of that a variable output high-pressure supply pump would be very desirable.
Furthermore, a speed range of a typical gasoline engine is substantially wider than that of diesel engines (e.g., from 500 RPM at idle to 7000 RPM or higher at rated speed). With variable pumping pressure it would be easier to optimize the injection rate at any engine speed.
Several configurations for a direct injection gasoline supply pump are shown and described in U.S. patent application Ser. No. 09/031,859, filed Feb. 27, 1998 for xe2x80x9cSupply Pump For Gasoline Common Railxe2x80x9d, the disclosure of which is hereby incorporated by reference. The present invention can be considered as particularly well suited for implementation in one or more of the embodiments shown in said application, as well as variations thereof.
According to the present invention, a high pressure pump provides both variable output and pumping pressure modulation. At a first level of control (gross modulation), the pump does not undergo high pressure pumping action, except when needed. At a secondary level of control (micromodulation), at least the frequency of actuation of an electrically operated, (e.g., proportional solenoid), is manifested as pumping pulses which produce the required average high pressure.
The invention can broadly be considered as a method for controlling a common rail gasoline fuel injection system having a high pressure supply pump to the common rail, wherein the improvement comprises recycling the pump discharge flow through the pump at a pressure lower than the rail pressure, between injection events, and restoring the discharge flow to the common rail immediately before the next injection event.
The invention may be better understood in the context of a gasoline fuel injection system for an internal combustion engine, having a plurality of injectors for delivering fuel to a respective plurality of engine cylinders and a common rail conduit in fluid communication with all the injectors for exposing all the injectors to the same supply of high pressure fuel. An electronic engine management unit includes means for actuating each injector individually at a selected different time, and for a prescribed interval, during each cycle of the engine. A high pressure fuel supply pump having a high pressure discharge passage is fluidly connected to the common rail, and to a low pressure feed fuel inlet passage. A control subsystem controls the discharge pressure of the pump between injection events, by diverting the pump discharge so that instead of delivery to the common rail, the flow recirculates through the pump at a lower pressure. This is preferably accomplished by an inlet control passage fluidly connected to the low pressure feed fuel inlet passage, a discharge control passage fluidly connected to the high pressure discharge passage, and a non-return check valve in the high pressure discharge passage, between the discharge control passage and the common rail, which opens toward the common rail. A control valve is fluidly connected to the inlet control passage and to the discharge control passage, and switch means are coordinated with the means for actuating each injector, for controlling the control valve between a substantially closed position for substantially isolating the inlet control passage from the discharge control passage and a substantially open position for exposing the inlet control passage to the discharge control passage.
The invention may also be considered a method for controlling the operation of a high pressure common rail direct gasoline injection system for an internal combustion engine, comprising continuously operating a high pressure fuel pump to receive feed fuel at a low pressure and discharge fuel at a high pressure to a check valve which opens to deliver high pressure fuel to the common rail. Sequentially, each injector is actuated, and after each injector actuation, an hydraulic control circuit is opened upstream of the check valve, whereby the pump discharge passes through the control circuit instead of the check valve, at a decreased pressure from the high pressure to a holding pressure between the high pressure and the feed pressure. While the pump discharge passes through the control circuit but immediately before each injector actuation, the hydraulic circuit is substantially closed whereby the pump output pressure rises from the holding pressure to the high pressure. When the pump output pressure reaches the high pressure an injector is actuated.